The present invention relates in general to the mounting of an instrument panel to a body cowl in a road vehicle.
A typical portion of the front end structure in cars, trucks, and other road vehicles which is at the interface between a passenger compartment and an engine compartment comprises a sheet metal body cowl set atop the firewall which supports a windshield and a front, upper section of an instrument panel substrate. The instrument panel substrate carries various elements such as driver instrumentation, climate control components, entertainment components, storage compartments, and airbag devices. Besides being supported at its top, front end by the body cowl, the instrument panel substrate is also supported at its middle and bottom sections by other body structures such as a cross-car beam.
An important consideration in designing a vehicle is the control of noise, vibration, and harshness (NVH). To help maintain good NVH performance, steel attachment brackets between the instrument panel substrate and body cowl act as spacers so that the instrument panel substrate can flex without significant interaction with the body cowl. By appropriately designing the steel brackets, target NVH levels can be achieved for each particular vehicle model. Generally, stiffness must be high in order to achieve a high NVH performance.
Very stiff brackets, however, may be undesirable from the standpoint of achieving a desired pedestrian protection. In an accidental impact between a vehicle and a pedestrian, stiffer surfaces at the vehicle's exterior can result in an undesirably high acceleration being applied to the impacting pedestrian. A structure which is more yielding (i.e., compliant) tends to produce lower injury by reducing the reaction forces seen by the impactor.
It is desirable for the body cowl to deflect downward in response to an impact against the hood or windshield. An overly stiff connection between the body cowl and the instrument panel substrate results in the instrument panel lowering the ability of the body cowl to deflect downward. Significant effort is required to determine a configuration of the steel brackets that achieves the conflicting demands of NVH and pedestrian protection. Thus, the known attachment system using steel brackets results in large inefficiencies in the design process, which is especially severe in an organization that designs vehicles for many vehicle model programs.